1. Field of the Invention
The present invention relates to a method of detecting nozzle clogging and to an analytical instrument. More specifically, the invention relates to a method of detecting clogging of a nozzle that draws in a sample and to an analytical instrument fitted with a device for detecting nozzle clogging.
2. Description of Related Art
In an automatic biochemical analyzer, a sample to be analyzed is drawn in by a nozzle and dispensed as aliquots. If the nozzle clogs up, the aspiration volume becomes inaccurate. Therefore, the nozzle is monitored at all times to detect whether the nozzle is clogged or not. The detection is done by comparing the nozzle pressure produced when the sample is drawn in with threshold values. See, for example, Japanese Patent Laid-Open No. 09-015248 (pages 3–4, FIG. 2).
The sample volume drawn in differs according to a different analytical item. The required aspiration pressure, i.e., the absolute value (hereinafter referred to as the nozzle pressure) of the differential pressure (normally, negative pressure) with the atmospheric pressure, differs according to a different aspiration volume. Therefore, it is necessary to prepare a different threshold value used for detection of nozzle clogging for each aspiration volume. Furthermore, even if the aspiration volume is constant, the required nozzle pressure varies depending on the degree of dilution of the sample and on the kind of sample. Consequently, it is also necessary to prepare a different threshold value for each set of dilution conditions and for each kind of sample. Moreover, if one attempts to make switchable the sensitivity at which clogging is detected, threshold values corresponding to plural sensitivities are necessary. To satisfy these requirements, required threshold values must all be preset. This needs a cumbersome and laborious operation.